Blood oxygen saturation is the relative amount of oxygenated hemoglobin in all of the hemoglobin present in the blood stream. This hemoglobin is packaged in biconcave discs of approximately 10 micrometers diameter which commonly occur with a density of approximately five million red blood cells per cubic millimeter. When radiant energy (e.g., light) is incident upon red blood cells, the red blood cells both scatter and transmit the incident radiant energy. The differential absorption by oxygenated hemoglobin (also known as oxyhemoglobin) and deoxygenated hemoglobin (also known as deoxyhemoglobin) of the radiant energy reflected by and transmitted through the red blood cells furnishes the basis for oxygen saturation measurements.
More specifically, pulse oximeters use light of two or more different centered wavelengths (e.g., produced by two or more light sources) to obtain measures of blood oxygen saturation by measuring the absorption and/or scattering of oxyhemoglobin and deoxyhemoglobin. The measured scattering data allows for the calculation of the relative concentrations of reduced hemoglobin (Hb) and oxyhemoglobin (HbO), and therefore blood oxygen saturation levels, since the scattering relationships are known.
While implantable pulse oximetry type oxygen saturation sensors have been proposed, it would be beneficial if such sensors can be used to measure more than just oxygen saturation. Further, it would be beneficial to increase the accuracy of such sensors.